1. Field of the Invention
The present invention is a recirculation path unit of a linear rolling bearing. The unit includes a linear loading passage, a linear unloading passage, and two directional reversing passages, which are connected to the linear loading and unloading passages, to form a closed recirculation path within which rolling elements perform an infinite motion. The methodology of designing the reversing passages of the present invention is based on the continuity of the curvature, which is expected to be able to vary from zero to an assigned value and vice versa, at the connecting points to the loading and unloading linear passages. As a result, not only the continuity of the slope of the tangential lines at the vicinity of the connecting points but also the continuity of the curvature of the whole circulation path can be ensured. The continuity of the curvature provided by the present invention eliminates abrupt changes in centrifugal acceleration at the spots where the rolling elements enter or leave the reversing passage, thus reducing the impact force acting on the wall of the directional reversing passage by the element, the sliding function forces and noise induced by the vibration under high-speed operation conditions.
2. Description of the Prior Art
The design of the conventional reversing passages for the rolling elements in a linear bearing emphasizes the direction reversing function, with the goal of making the curves be tangent to each other at the connecting points, by forming the reversing passages through the connection of straight lines, circular arcs or elliptic arcs in order to cause the slope to be made the same at the connecting points. However, from a dynamic point of view, failure to take into account the continuity of a curvature at the connecting point, results in an abrupt change in the centrifugal acceleration and a tremendous impact force that acts on the turning wall, inducing sliding function, vibrations, and noise for a rolling element moving with a high speed in the reversing passage.
U.S. Pat. No. 4,296,974 provides an example of such a structure, which is illustrated in FIG. 11A of the present application where a reversing passage 1 consists of a semi circular arc with radius R and the passage is tangent to the other two linear passages in the connecting points. As the rolling element 2 moving from the loading passage 3 to the circular arc 1, the curvature of the passage changes abruptly from zero to 1/R at point B. Similarly, the curvature of the passage changes also abruptly from 1/R to zero at point C. Besides the above mentioned semi circular arc, a reversing passage design composed of two pieces of one-quarter circular arcs and a piece of straight line segment is disclosed in U.S. Pat. No. 4,505,522, which is represented by FIG. 12A of the present application. Although the slopes of these two reversing passages of this design are continuous at the connecting point, the inferior characteristic of the convention design such as the impact force, sliding function, vibration and noise caused by ignorance of the continuity of the curvature at the connection point remain the same. This can be seen through the curvature variation of these cases shown in FIGS. 11B and 12B.
An effort to improve the conventional design is disclosed U.S. Pat. No. 4,652,147, in which two or more curves with different curvatures are used to design the reversing passage circuit in a linear bearing structure. It can be seen from FIGS. 13A and B, and 14A and B of the present application that the passages are basically formed by arcs with smaller curvatures to larger curvatures. Although the difference of the curvature is reduced at the connection points, the curvatures remain mismatched i.e., discontinuous, at those points. In the same patent, a design using an elliptic arc to replace the circular arc is also suggested as shown in FIG. 15A. In this design the difference between the curvature of the connecting lines is further reduced; however, the improvement is limited because the discontinuity in the curvature is the same as other conventional designs. This improvement can not be used to effectively reduce the impact load, sliding function, vibration, and noises. The curvature variation of this case is plotted in FIG. 15B for reference.
Linear ball bearings including the linear Guideway, the linear ball bush, and the ball spline are widely used in modem mechanical, semiconductor and automation industries. Because of the demands of high efficiency in manufacturing, the speed requirement of the linear bearing is much higher than the conventional practice. Under this high-speed requirement, the issues of impact, sliding function, and vibration and noise become more and more significant. The conventional design of the reversing path of a linear bearing pays attention simply to the continuity of the slopes of tangent lines at a connecting point. Thus the reversing circuit is mostly made through the composition of straight lines, circular arcs or elliptical arcs with the same tangent at the connecting points. Though the slopes are continuous, the curvatures are not continuous at the connecting points. At the place where the rolling element moves from the linear straight passage to the circular arcs, the radius of the curvature changes rapidly so that it causes the rolling element to turn direction abruptly and a centrifugal acceleration to appear instantaneously. It will also induce extra impact and functional force by the abrupt change in the direction of the rolling element. On the other hand, because of the discontinuity of the curvature at the connecting point the rolling element will have unfavorable jerking, colliding and jostling when passing through the spot of the connection, and will have a less smooth motion and generate enormous noise resulting in a reduction of the mechanical efficiency.